1. Field of the Invention
This invention relates generally to a magnetoresistive sensor, and more particularly to such a sensor based on extraordinary magnetoresistance (EMR).
2. Description of the Related Art
A magnetoresistive sensor based on extraordinary magnetoresistance (EMR) has been proposed as a read-head sensor for magnetic recording hard disk drives. Because the active region in the EMR sensor is formed of nonmagnetic semiconductor materials, the EMR sensor does not suffer from the problem of magnetic noise that exists in read-head sensors based on giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR), both of which use magnetic films in their active regions.
The EMR includes a pair of voltage leads and a pair of current leads in contact with one side of the active region and an electrically conductive shunt in contact with the other side of the active region. In the absence of an applied magnetic field, sense current through the current leads passes into the semiconductor active region and is shunted through the shunt. When an applied magnetic field is present, current is deflected from the shunt and passes primarily through the semiconductor active region. The change in electrical resistance due to the applied magnetic field is detected across the voltage leads. EMR is described by T. Zhou et al., “Extraordinary magnetoresistance in externally shunted van der Pauw plates”, Appl. Phys. Lett., Vol. 78, No. 5, 29 Jan. 2001, pp. 667–669. An EMR sensor for read-head applications is described by S. A. Solin et al., “Nonmagnetic semiconductors as read-head sensors for ultra-high-density magnetic recording”, Appl. Phys. Lett., Vol. 80, No. 21, 27 May 2002, pp. 4012–4014.
One of the problems of the EMR sensor is that its magnetoresistance is an approximately quadratic function of the applied magnetic field. Thus the magnetoresistance response is small and nonlinear in the presence of the small magnetic fields from the recorded magnetic media. Biasing of the EMR sensor has been proposed by an asymmetric location of the voltage leads. Biasing of the EMR sensor has also been proposed by use of a single ferromagnetic layer that applies a perpendicular magnetic field to the sensor, as described in U.S. Pat. No. 6,714,374.
What is needed is an EMR sensor with improved magnetic field biasing so the sensor has higher magnetoresistance in small applied magnetic fields and a more linear response to the applied magnetic field.